Conventional electric fans were either of the structure of using a wind direction shifting plate without moving the fan head itself to change the direction of the wind generated by the fan impellers, or of the structure of mounting a fan impeller coaxially to the motor and swinging the fan head from left to right and vice-versa by a certain fixed crank device.
Accordingly, these conventional electric fans displayed the problem of not sending wind to all directions, thus leaving the other side with no wind in a hot state.
To overcome this problem, the inventor of the present invention proposed an electric fan in the Korean Utility Model Publication No. 89-1902 (U.S. Pat. No. 4,922,766) employing a plurality of fan impellers, e.g. three impellers that are detatchably connected to the driving motor, each of said fan impellers being arranged with 120 degrees in radial direction and driven individually or simultaneously by using the fan clutch device, thus sending the wind to 360 degrees in all directions.
However, said previously invented electric fan not only had an inefficiency of driving force transmission due to the flat surface of the friction face of both the driven bevel friction wheel which is located at one end of the fan impeller shaft and the driving bevel friction wheel which is located at one end of the driving motor shaft, but did not have any means for controlling or adjusting the slanted angle of the fan impeller in vertical movement and, thus, sent no wind to the up-and-down direction.
Another problem raised in the previously invented electric fan is a blowing reaction which makes the fan head be biased to right or left. That is, since an electric fan which is in general formed by a plurality of helical fan blades, is a device which sends the wind to the front of the fan impeller by turning the fan impeller rapidly, the fan impeller receives some blowing reaction during operation due to the direction of the helical fan blades. The previously invented fan was so implemented as to have three fan impellers and, therefore, if all the fan impellers were blowing the wind and turning simultaneously in one direction, the blowing amount of wind will increase and so will the blowing reaction as much. That is, when the fan impellers were turning in one direction, e. g. to the left by the operation of a crank device while still blowing, the blowing reaction will be added to its turning force to the left, thus, the turning speed will increase. On the other hand, when the fan impellers were turning to the right, the blowing reaction will work against the turning force, and this resulted in some vibration to the fan impeller itself and an excess load on the driving motor.
Further, since the fan clutch device of the previously invented electric fan is of a screw type, some inconvenience in manipulating the shaft clutch device due to incurrence of some extra time, resulted.
And also, since the previously proposed electric fan has three fan impellers, the total weight thereof becomes too heavy to move around and also since the control switch was provided on the lower body, which works as a support for the upper body, the upper body could not be separated from the lower body and, thus, it could not be constructed as a short up-right standing type and/or an attach-to-ceiling type and/or an attach-to-wall type.